Colicins are highly effective cytotoxins. A single bound molecule can kill a cell. Several different approaches have been applied to understanding the mechanism of action of the 190 residue colicin E1 in terms of protein structure. The variety of biophysical studies that have been performed on the membrane associated form of colicin E1 have led to widely differing structural models, some of which contradict each other. The presence of trans-membrane helices in the functional form of colicin E1 is a crucial point, since it has strong implications for the structural organization and mechanism of action of the protein. The solid-state NMR experimental approaches being developed at the Resource are able to address this issue particularly well. Uniformly 15N labeled colicin E1 was prepared at Purdue University by expression of the plasmid encoded gene in bacteria. The unoriented spectrum of uniformly 15N labeled colicin E1 in bilayers is of a 15N amide chemical shift anisotropy powder pattern with some relatively narrow resonance intensity superimposed at the isotropic chemical shift frequency. This is exactly the result expected for a typical membrane protein where most of the residues are rigidly held in helices and some of the residues, most likely those at the N- and C- termini and in loops connecting the helices, are mobile. More interesting results emerge from the experiments on samples of the protein in bilayers oriented between glass plates. Since the secondary structure of the protein is known to be primarily alpha helix, these resonance bands indicate that the protein had both trans-membrane and in-plane helices. These results indicate that colicin E1 is a typical membrane protein that has the potential to form channels with its trans-membrane helices.